During drilling operations for the extraction of hydrocarbons, a variety of recording and transmission techniques are used to provide or record real-time data from the vicinity of a drill bit. Measurements of the surrounding subterranean formations may be made throughout oil drilling and exploration operations using downhole measurement and logging tools, such as measurement-while-drilling (MWD) and/or logging-while-drilling (LWD) tools, which help characterize the formations and aide in making operational decisions.
The downhole measurement and logging tools obtain image data, such as, azimuthal density data, AFR (azimuthal focused resistivity) data, ADR (azimuthally deep resistivity), azimuthal acoustic compressional and shear images, acoustic borehole caliper and reflectance, spectral natural gamma ray and non-spectral natural Gamma imaging. The image data is typically transmitted to a surface using mud pulse telemetry techniques. Such techniques are often limited to line-by-line processing, such as, data compression being performed on a row-by-row basis. Transmission of such data typically corresponds to a stringent delay limitation.
Many image compression techniques cannot be applied due to the short length of the data required for uphole transmission. In one approach, compression of image data is based on an assumption that physically adjacent measurements have high probability of being correlated. However, the differences between the adjacent measurements would yield a smaller dynamic range. In another approach, delta modulation provides that when one of the differences in a row of measured data is decoded incorrectly, subsequently decoded elements may not be reconstructed correctly. Secondly, such differences carry only local information. In addition, the decoded values based on delta modulation tend to be more randomly located. As such, structures of formation events cannot be readily reconstructed without a burden on existing compression algorithms.